Mighty River Power's management faced accusations of giving ''smart arse'' answers ahead of their appearance before a Parliamentary select committee this morning.

Opposition MPs on the commerce select committee said Mighty River Power, which is expected to float in the coming months, only answered 37 of 133 written questions supplied to it, refusing to answer many which the likes of Genesis Energy had decided to.

Labour MP David Clark said Mighty River had refused to answer a question on whether there had been a restructure in the past 12 months, because the question referred to a ''government department'' not a state owned enterprise, and so it was ''not applicable''.

''You could see how that would be considered as a sort of smart arse answer by someone being uncharitable with their language,'' the Dunedin North MP said

Clark said the lack of answers meant the committee could not effectively do its job on behalf of taxpayers to provide Parliamentary oversight.

Later Green MP Gareth Hughes said he was disappointed at what he said were ''frankly disdainful'' answers, with Mighty River refusing to say how many credit cards the company had, or how much floor space it leased.

Only National MP Sam Lotu-Iiga came to the defence of Mighty River MPs, saying the wording of the questions was ''lazy''.

Outside the hearing, Mighty River chairwoman Joan Withers defended the company's answers and said if they were rephrased they would answer accordingly.

''There was absolutely no intention to treat the committee with disdain and as we said to the committee we will re-look at those questions and go back. Certainly the phrasing of the questions I think, as the National Party committee members pointed to weren't detailed enough or didn't ask about SOEs specifically.''

Chief executive Dough Heffernan confirmed the number of credit cards to reporters.

''It's not a big deal. Indeed I can tell you live right here that we have three credit cards in the company that are held for office administration expenses. No employee has a credit card.''

He declined to say whether he agreed the answers were ''smart arse''.

Withers said; ''I think what you can take out of this is absolutely no intention to thwart the process or to be smart alec''.

The Mighty River bosses refused to answer a number of questions on the grounds that they were in a pre-prospectus period, so were prevented from doing so because of the Securities Act.

The Government plans to sell up to 49 per cent of the company by the middle of this year.